I've disussed hydration while riding in hot conditions with my doctor, and he advises that plain water is fine, drink befiore you are thirsty, but add anything to the water and it will absorb into your body much quicker than straight water alone. You can add a squeese of fruit juice, a pinch of sports drink powder (what I do), a splash of cordial, a dash of lemonade...... they will all work.